PERHAPS
there is no animal on this planet that can exist without any contact
with the fellow members of its species. There are few needs that no
living being can ignore, and passing one’s genes to the next
generation is one of them.

At some time in the lives
of the great majority of animals, the sexual products of the male must
find those of the female for the purpose of reproduction. In such a
situation, it is not surprising to find that creatures of the opposite
sex act in such a way that the behaviour of the other animal is altered.
The special behaviour thus produced is mating. Even the most inactive
animals can’t remain uninfluenced in such circumstances.

For instance, sea-urchins,
relatively inactive sea animals, are influenced by others; the release
of sexual products into the sea by one member of the species stimulates
the others to discharge their eggs or sperm likewise. This is
communication by chemicals.

In this way, the act of
courtship reveals clearly the kind of information that may be
transmitted from one animal to another. For the phenomenon to work
efficiently, it is important that the species must first be identified
so the signal must preferably be one which is unique to that species;
secondly, the sex of the animal has to be signalled. Thirdly, the
physiological state of the animal - in this case, its readiness to mate
- must be conveyed, and finally, its position given, for if it is to be
located by the other animal it needs to indicate where it is. This is a
good example of the range of information that can be conveyed by a
relatively simple act of an animal.

The Siamese fighting fish changes colour on seeing a rival

Sent by a sender and received by a receiver, the essence of communication is a
signal that bears information and it can be in any form that the receiver can
sense. There are visual, auditory, touch and chemical signals that the animals
use to communicate, but each kind has its own advantages and disadvantages,
making one suitable for one way of life and another adapted to some other
habitat.

Even the colours have
communication value, that is why some animals, insects, fish and birds have
bright colours. For instance, black and yellow stripes on a wasp’s body, serve
as warning signals marking out distasteful prey to possible predators; birds too
learn to avoid cinnabar moth caterpillars, bearing same kind of stripes, after
their first unpleasant encounter with them. Some colours help animals in
camouflaging, but very many hues are useful for display which make an animal
conspicuous to its species mates. One of the many examples is the male of the
Siamese fighting fish that turns to brilliant bluish colour on seeing a rival.
In birds coloured plumage, tufts and patches of feathers are displayed during
the courtship movements.

Some of the most amazing are the
feathers and plumes of birds of paradise. Ribbon-tailed bird of paradise trails
a pair of two-foot long white feathers, tipped with black, from its tail. But it
is not only the splendid colours and their patterns that are used for display
purposes in animals, the pattern or sequence of movement of some part of the
body may also play important role during courtship. For instance, different
species of fiddler-crabs can be distinguished by the way in which their enlarged
claw is raised and brought down again - the gestures of a male attempting to
lure a female. These signals are so distinctive and species-specific that as
many as five species live side by side on the same beach without creating any
confusion in the population.

Fireflies, insects that are active
only in the night, too use visual signals by flashing light produced at special
spots on their abdomens. Males of one common species flash lights in a short
series of ‘Morse’ dots, and the female responds by flashing her lights
exactly two seconds after the end of the male’s signal. Males respond by
heading towards the female. In experiments it has been proved that the male will
only move to lights that are flashed at exactly the right time interval after
the end of his. This light code ensures that the females, only of his own
species, should attract the male.

Facial expressions also play a
great part in communication not only in humans, but in animals too. In monkeys
and apes ‘smile’ with teeth exposed or covered by lips makes a lot of
difference in conveying information.

This shows that visual signals are
of varied forms, but they all require sender and receiver to be in view of each
other. It means that in most of the cases both of them will have to come out of
the cover in open, exposing them to danger from watchful eyes of predators.
Advantage of the system is that the signals can be visible over a great
distance, but when it is employed, perhaps, its possible disadvantages have been
weighed, by natural selection, against the advantages and found wanting.